Method of controlling density in gas-sensitized aqueous explosives

ABSTRACT

A process for controlling the density of a gas-sensitized aqueous explosive. The components of the explosive are intermixed to form a continuous stream, one of the components being a gasretaining component. The portion of the stream containing the gas-retaining component is passed through a mixing zone across which there is a pressure drop of at least 5 p.s.i. The gas is added to the mixing zone and is homogeneously dispersed into the stream.

United States Patent Conrad [15 3,642,547 Feb. 15,1972

[54] METHOD OF CONTROLLING DENSITY IN GAS-SENSITIZED AQUEOUS EXPLOSIVES [72] Inventor: Keith L. Conrad, Tamaqua, Pa. [73] Assignee: Atlas Chemical Industries, Inc., Wilmington, Del.

[22] Filed: June 10, 1969 [21] Appl. No.: 831,895

[52] U.S.Cl ..l49/2, 149/60, 149/74 [51] Int. Cl. ..C06b 19/00 [58] FieldofSearch ..149/2,41,43,44, 46, 60,

[56] References Cited UNITED STATES PATENTS 3,288,658 11/1966 Ferguson et a1. ..149/2 3,288,661 11/1966 Swisstack ,.l49/2 X 3,419,444 12/ 1968 Minnick 149/2 3,449,181 6/1969 Armantrout et al. ....l49/44 X 3,453,158 7/1969 Clay ....149/44X 3,522,] 17 7/1970 Atadan et a1 149/2 X 3,523,048 8/1970 Hopler 149/44 X Primary Examiner-Carl D. Quarforth Assistant Examiner-Stephen J. Lechert, Jr. Attorney-Kenneth E. Mulford, Roger R. Horton and Ernest G. Almy [57] ABSTRACT 14 Claims, 3 Drawing Figures PAIENIEDFEB 15 m2 5 7 SHEET 1 BF 3 cv cv -1gy1|-{ |w3 H H M- e. I PG ca CS l FIG. I

INVENTOR ATTORNEY METHOD OF CONTROLLING DENSITY IN GAS- SENSITIZED AQUEOUS EXPLOSIVES SUMMARY This invention relates to the production of aqueous explosives of controlled density. Specifically, it relates to the sensitization of an aqueous explosive by homogeneously mixing a gas into an explosive stream in a mixing zone across which is a pressure drop of at least 5 p.s.i.

BACKGROUND OF THE INVENTION Although it has been known for some time to add air to such aqueous explosives as emulsion and slurry explosives in order to decrease their density and therefore to increase their sensitivity, these methods often have bothersome problems associated with them. Using a batch process, the explosive is prepared in an open vat and air at atmospheric pressure is blended in with a mixer. After a homogeneous mix has been obtained, the density of the mix is taken to determine whether the proper amount of air has been retained in the mix. If the mix contains insufficient air, it is frequently necessary to repeatedly remix, and even reheat the mix, and then retest the density until the proper concentration is obtained; thus, it is very much a trial-and-error method.

In the continuous method, the air is injected into the explosive stream; a crude control of the density results, but the explosive rapidly increases in density and becomes insensitive (undetonable) on storage. Moreover, this process requires a thickener to hold the air in the explosive. Even with the thickener, an explosive sensitizer such as smokeless powder is required in addition to the air to sensitize the explosive.

In addition, in both the batch and continuous processes, a gas is not retained by the explosive above a certain temperature known as the foam point." Since the foam point may be less than the temperature at which some ingredients of the mix begin to crystallize (the crystallization temperature), many emulsion and gel explosives which are partially or wholly dependent upon aeration to attain detonability cannot be formed at temperatures above the foam point and still be detonable. Thus, some means other than the addition of air has to be used to sensitize these emulsion and gel explosives.

ADVANTAGES OF THE INVENTION 1 have invented a method of controlling the density of a gassensitized aqueous explosive composition which permits precise and virtually instantaneous control of the density. My process does not require the presence of a thickener nor of a sensitizer other than a gas. Thus, additional ammonium nitrate may be substituted for the absent thickener and the explosive sensitizer. The absence of the explosive sensitizer results in a lower cost explosive and a safer explosive composition since the explosive composition is less sensitive to detonation and usually cannot be detonated in the absence of the gas. Moreover, in my process, the gas does not agglomerate rapidly after the explosive is made. Products made according to this invention have been stored over a year without excessive gas agglomeration resulting in desensitization. Finally, my method makes possible the formation of many emulsion and gel explosives which have crystallization temperatures above their foam points. Air can now be added considerably above the foam point of the explosive and, in many cases, at a temperature which is above the crystallization temperature. In fact, the air can often be added at a temperature far enough above the crystallization temperature to permit the crystallization temperature to be raised by increasing the concentration of the dissolved materials which precipitate below the crystallization temperature; since these dissolved materials usually consist of nitrates such as ammonium nitrate, the power of the explosive can in many cases be increased by my process.

The major advantage of my processes, however, is the capability of predetermining and accurately controlling the product density. The density of the product may be changed almost instantaneously by changing the flow rate of the gas stream entering the system. The time required to obtain the change in product density is the residence time in the mixing zone plus the time required to displace the product in the discharge line from the mixing zone. A distinct advantage of accurate density control and rapid density change is illustrated by FIG. 3, which is a set of curves showing how density affects detonation pressure and velocity. The two curves of FIG. 3 were developed using the composition of Example I] and the process of FIG. 1, hereinafter described. Since detonation velocity and pressure are measures of the detonating energy, the dependence of detonation velocity and detonation pressure upon density permits predictable and direct control of the explosive energy of the product, thereby providing a means of varying the energy of the product to suit various individual blasting requirements. FIG. 3 also shows that this explosive composition was not detonable at a density over 1.33 where detonable means with a primer charge such as 2.35 pounds of Power Primer" sold by Atlas Chemical Industries, Inc.

DESCRIPTION OF THE INVENTION In my process, the components of the gas-sensitizable aqueous explosive are intermixed to form a continuous stream. One of the components of the explosive, preferably the fuel, is capable of retaining a sufficient amount of gas therein to sensitize the explosive, such a component being herein referred to as the gas-retaining component." This component has a high viscosity, generally of at least about 1,000 centipoises at 68 F. In order to simplify the system and the number of components which must be controlled, the gas-retaining component is preferably a fuel such as paraffin wax, microcrystalline waxes, bunker-C oil, and other high flow-point oils. Fuels of lesser viscosity such as ethylene glycol, mineral oil, corn oil, and castor oil are not suitable as gas-retaining components. The gas-retaining component must be present in sufficient quantities in the explosive to sensitize it; generally, if about 0.5 to 15 percent (all percentages herein are by weight) of the explosive is a gas-retaining component, the explosive can be sensitized by my methods.

The gas-retaining component, either by itself or as part of the stream, is passed through a mixing zone across which there is a pressure drop of at least 5 p.s.i. and preferably at least 25 p.s.i. The pressure drop across the mixing zone is essential to the functioning of this invention since without it the gas agglomerates and does not sensitize the composition.

A sufficient amount of a gas, preferably air, to sensitize the explosive is added to the mixing zone either directly or carried in a component. Best results are obtained when the gas pressure exceeds the stream pressure at the point of addition of the gas by at least 5 p.s.i. and preferably 25 p.s.i. In the mixing zone the gas is dispersed homogeneously throughout the stream. The stream in the mixing zone, if it is not the entire stream, should then be thoroughly mixed with the remaining components. The stream is then discharged into a borehole, packages, or a storage tank. The stream at discharge should preferably exceed atmospheric pressure by at least 5 p.s.i. and preferably at least 25 p.s.i. for best results. The stream should be discharged below the foam point to prevent gas agglomeration.

It has been found that still better density control is obtained when the flow of the gas into the mixing zone is maintained at a constant rate regardless of variations in downstream pres sure. This can be accomplished, for example, by monitoring the downstream pressure and automatically varying the pressure of air admittance in accordance with this downstream pressure. This eliminates variations in the density due to adding extra hose at the point of discharge, temperature variations, viscosity variations, etc.

The amount of gas necessary to reduce the density of an explosive to a desired level can be easily calculated. For example, if 1.0 c.f.m. of a water emulsion explosive having a density of 1.40 g./cc. is passed through a mixer, and it is desired to reduce the density to 1.15 g./cc., the required rate of addition of air to the mixer is 0.2177 s.c.f.m. The following calculations are applicable to this example:

62.43 lbs/cu. ft. 1.4=87.4 lbs/cu. ft.-Initial feed rate and density.

62,43 lbs/cu, ft. X l. 15= 71.8 lbs/cu. ft.Desired product density.

lb./cu. ft.=0.01144 cu. ft. /lb.-Vo1ume per pound of feed.

lb./cu. n..=o.1393 cu. ft./lb.Desired volume per pound of product.

The maximum amount of air which the products can be made to retain is dependent upon the composition and temperature of the products. However, maximum aeration is not normally required to obtain a detonable product.

This invention applies to aqueous explosives which means explosives containing at least percent water such as slurry, emulsion, and gel explosives. Aqueous explosives generally contain an oxidizing solution and a modification agent in addition to a fuel component. The oxidizing solution is a solution of nitrates or perchlorates such as ammonium nitrate, sodium nitrate, potassium nitrate, calcium nitrate, or potassium perchlorate; ammonium nitrate is most commonly used and is preferred because it is least expensive. The fuel is any oxidizable material such as carbon or fuel oil. The modification agent is an emulsifier for an emulsion, a gelation agent for a gel, and a stabilizing agent for a slurry, although slurries may not always require a modification agent as Example IV illustrates. The gas is preferably air; but carbon dioxide, nitrogen, oxygen, or other gases compatible with the composition being processed could also be used.

DRAWINGS FIGS. 1 and 2 are flow diagrams illustrating two of the many possible ways of carrying out the process ofthis invention.

In FIG. 1, an oxidizer solution and a fuel blend are prepared and stored, until used, in tanks T, and T respectively. These two tanks are suitably equipped for agitation and temperature control. The oxidizer and fuel are then pumped through the processing system by pumps P, and P which are compatible with the ingredients in use and capable of maintaining the required flow rates at the pressures involved. Moyno progressive cavity pumps were used in the examples which follow, but any other suitable pump would be satisfactory.

The pressure relief valves PRV, and PRV provide protec-- tion for the processing equipment in the event of a downstream line blockage resulting in excessive pressure buildup in the system. These valves are shown relieving to their respective material storage tanks T, and T for the purpose of material salvage.

The flow meters M, and M placed in the oxidizer solution and fuel blend feed lines, respectively, function in two capacities. The first is as a check on the flow rate. The second is as a control sensor which responds to flow rate changes and transmits the primary signal, in a control loop, which controls the pumps P, and P to maintain the required flow rates.

The check valves CV,, CV and CV, assure directional flow of the individual streams.

The supply of gas used for density control is shown as item A. Any source of gas is satisfactory if the required pressure and volume are supplied.

PC is a pressure control device which controls the supply gas pressure to the system at the desired level. PG is a pressure gauge which indicates the inlet pressure from the gas supply to the system.

The pressure relief valve IRV serves the same function as PRV, and PRV It is shown relieving to the atmosphere D.

The gas flow rate is controlled by valve GV and metered by the meter M The meter M may or may not control the gas flow by controlling the valve GV.

The item BPR is a back-pressure regulator which maintains a constant flow of gas through varying downstream pressures. This item assures positive delivery of the required rate of gas to the system.

The pressure gauges G, and 6, provide visual determination of the pressure drop across the mixer. The item V is a valve which controls the pressure drop across the mixer by constricting the discharge area. Although almost any type of valve may be used, an air-operated, pinch-type valve is satisfactory.

The mixer MXR is any mixer suitable for the ingredients and application intended to be used in the process. Three commercially available mixers are cited in the following examples. The cited mixers illustrate the wide range of mixing shear adaptable to the system but do not limit the system to the use of any specific mixer. The mixer may or may not be equipped for heat transfer, as required by each specific application.

If heat transfer is required, as in Example VII herein, the heat transfer medium is made available at the supply CS and is transferred through the heat transfer system C]. The heat transfer medium may be recycled or discharged, CD, as required by the system. The design of the heat transfer system is controlled by the design ofthe individual mixer in use.

The items PE and BL refer to systems of packaging equipmentor direct borehole loading, whichever is applicable.

In FIG. 2, the process illustrated is identical with FIG. 1 except for the following additions and modifications:

A second mixer CMR is added to the system to l) accomplish additional heat transfer if the heat transfer capacity in the mixer MXR is inadequate and (2) permit the incorporation of additional ingredientsafter preliminary processing has been accomplished. A second supply of heat transfer medium 5 has been added. However, both mixers could be supplied by the one system if the capacity is adequate. The use of this system is described in Example VII of this application.

The point of gas addition to the system, as illustrated in FIG. 2, may be after the first mixer MXR and before the second mixer CMR or before the first mixer MXR, as shown by the broken line. Either position is satisfactory if the required process pressure drops are maintained. If the gas is added between the two mixers, the second mixer CMR must be capable of adequately distributing the gas throughout the entire product mass.

An additional pressure gauge G has been added to provide a pressure indication between the mixers to assist in control of process pressures.

Other additions to the system such as tracing and jacketing of tanks and process lines, valving of process lines, piping configurations, use of recycle lines to increase the ease of startup and shutdown, use ofdirectly piped cleaning fluids to facilitate cleanup, and others, which would be apparent to individuals versed in the design and operation of such systems, have not been included for the sake of clarity.

The process of this invention as illustrated in FIG. 1 can be and has been successfully adapted to a mobile unit such as a truck. In addition to versatility, greater safety is achieved since the components are stored in separate tanks on the mobile unit and need not be mixed until the mobile unit is at the borehole. This truck mounted system has been used to process the compositions described in Examples II and III at rates up to 200 ppm.

Advantages of the processes illustrated in FIGS. 1 and 2 include the ease of operation attained by minimizing the number of control pointsonly the mixer speed, pressure control valve, and flow rates need to be adjusted to attain satisfactory operation. The product rate is easily changed during operation by simply increasing or decreasing the flow rates of the various streams. This can be accomplished in less than 1 minute when variable speed drive motors are utilized on the solution pumps. The product rate is limited only by the size of the processing equipment. The processes of FIGS. 1 and 2 are readily adaptable to the various types of aqueous explosives,

EXAMPLE 1 Acid-Based Emulsion An emulsion explosive containing 45.0 percent ammonium nitrate, 45.0 percent nitric acid of 60 percent strength, 1.0 percent acid-resistant, water-soluble, gel-forming polymer capable of cross-linking, specifically a 50-50 percent copolymer of methyl vinyl ether and maleic anhydride, 2.5 percent refined mineral oil, 4.0 percent refined paraffin, and 3.0 percent water-in-oil surfactant, specifically sorbitan monolaurate, was prepared as follows.

The ammonium nitrate and polymer were dissolved into the nitric acid at 105 F. to form Solution A. The remaining components were mixed at 125 F. to form Solution B; the temperature of Solution A was 8 F. below the foam point of Solution B. Solutions A and B were then pumped with Moyno progressive cavity pumps at 60 p.s.i. into a Votator CR highshear mixer and emulsified with enough air at 100 p.s.i. to lower the density from 1.40 g./cc. to between 0.90 and 1.35 g./cc. The back pressure across the mixer was maintained at 10 p.s.i., and the emulsion was produced at a temperature of about 1 10 F. The polymer cross-linked on storage to produce a stable product; the product was stable and detonable.

EXAMPLE ll Emulsion An emulsion explosive containing 41.5 percent ammonium nitrate, 45.0 percent nitric acid of 60 percent strength, 3.5 percent sodium nitrate, 4.0 percent acid-resistant mineral oil, 5.0 percent acid-resistant refined paraffin wax, and 1.0 percent ac id-resistant surfactant capable of forming a water-in-oil emulsion, specifically tri-decyl phosphate, was prepared as follows.

Solution A was formed by dissolving the ammonium and sodium nitrates in the nitric acid at about 90 F., above the crystallization point of the dissolved solids. Solution B was formed by combining the oil, wax, and surfactant at about 120 F.; the foam point of solution B was about 107 F. Solutions A and B were combined to form a stream at 90 F. Air was homogeneously dispersed into the stream as in Example 1 at 125 p.s.i. The stream was discharged at 75-80 p.s.i. (25 p.s.i. pressure drop across mixer). The density was lowered from 1.43 to 1.20. The maximum storage time had not been reached after over 1 year when the product had still not formed agglomerated bubbles and was detonable.

This example was repeated with a stream pressure of 35 p.s.i., an air pressure of 100 p.s.i., and a discharge pressure of 25 p.s.i. (10 p.s.i. pressure drop across mixer); similar results were obtained.

EXAMPLE Ill Emulsion The explosive prepared contained 54.0 percent ammonium nitrate, 20.0 percent sodium nitrate, 20.0 percent water, 3.0 percent microcrystalline wax, 2,0 percent mineral oil, and 1.0 percent of a surfactant comprised of monoand di-glycerides of fatforming fatty acids.

The ammonium and sodium nitrates were dissolved into the water at about 103 F. which was above the crystallization temperature but about 5 F. below the foam point of Solution B. The wax, oil, and surfactant were then combined at about 120 F. to form Solution B. Solutions A and B were processed as in Example 1 to form a mixture at 107 F. The air pressure was 100 p.s.i., the stream pressure, 60 p.s.i., and the discharge pressure, 50 p.s.i. (l0 p.s.i. pressure drop across mixer). The

density dropped from 1.43 to 1.15. The bubbles in the product did not agglomerate excessively and the product was detonable after storage for 270 days.

EXAMPLE lV Slurry Example 1 was repeated but the temperature of Solution A was held at F. which was below its crystallization tempera ture. Solution A was vigorously agitated to keep the distribution of undissolved solids homogeneous and was processed with Solution B at 125 F. to produce a slurry at F. and 60 I p.s.i. with a foam point of 113 F. The air pressure was 100 p.s.i. and the discharge was at 50 p.s.i. (l0 p.s.i. drop across mixer). The density dropped from 1.43 to 1.20. The product was stable and detonated after over a year of storage.

Example V Emulsion EXAMPLE Vl Emulsion 104 F. and a density of l. 16 g./cc. The product was stable and detonable.

EXAMPLE Vll Emulsion The explosive prepared contained 57.0 percent ammonium nitrate, 17.0 percent sodium nitrate, 20.0 percent water, 2.5 percent refined mineral oil, 2.5 percent of a microcrystalline wax and 1.0 percent of a surfactant comprised of monoand di-glycerides of fat-forming fatty acids.

The ammonium nitrate and sodium nitrate were dissolved into the water to form Solution A at 1 15 F. The crystallization point of Solution A was approximately F. The mineral oil, wax and surfactant were combined to form Solution B at 1 15 F. The foam point of Solution B was approximately 1 10 F.

The solutions were processed through the system depicted in FIG. 2 in the following manner.

Moyno progressive cavity pumps were used to pump Solutions A and B, individually, through a Votator CR mixer, where emulsification and aeration were accomplished, and then through a Votator scraped-surface heat exchanger, where the product temperature was reduced to a temperature below the foam point of Solution B. The following operating conditions were applicable.

The gas supply pressure was 100 p.s.i. The temperature of the product discharging from the Votator CR mixer, MXR in FIG. 2, was approximately 1 13 F. The density of the product stream was 1.15 g./cc. at the discharge of the Votator CR mixer as compared with 1.43 g./cc. at the inlet to the Votator CR mixer. The pressure on the inlet side of the Votator CR mixer was 80 p.s.i. (G in FIG. 2) and the pressure on the discharge side was 50 p.s.i. (G in H0. 2).

The product was cooled as it passed through the Votator scraped-surface heat exchanger (CMR in FIG. 2) from an inlet temperature of 113 F. to a discharge temperature of 107 F. The cooling water flow rate was 40.0 p.p.m. and the cooling water inlet and discharge temperatures were 65 F. and 69 F., respectively. The pressure in the inlet product line was 50 p.s.i. (G in FIG. 2) and the pressure in the discharge line was 30 p.s.i. (G in FIG. 2). The density of the product as it discharged from the Votator scraped-surface heat exchanger was 1.15 g./cc. The product was stable and detonable.

EXAMPLE VIII The components of Example II were prepared in the same manner as in Example II but were processed under the following conditions.

Solutions A and B were combined to form a stream at 90 F. Air, at a supply pressure of 100 p.s.i., was introduced to the stream at the inlet to the Votator CR mixer and was homogeneously distributed throughout the stream by the mixer. The density of the stream was thereby lowered from 1.43 g./cc. to 1.25 g./cc. at the product discharge. The pressure in the stream was 80 p.s.i. at the mixer inlet and 50 p.s.i. at the mixer discharge. The product temperature was 95 F.

Without altering any of the other system variables, the air flow rate was increased, lowering the density of the stream from 1.25 g./cc. to 1.15 g./cc. at the product discharge. The length of time required to obtain the change in density of the discharging product was approximately equal to the residence time in the mixer and the discharge line, 7.0 seconds. Other operating variables, temperatures and pressures, were essentially unchanged.

The products of these two operating conditions were stable and detonable, and the explosive characteristics of the two products were used in the development of the data for FIG. 3.

What is claimed is:

1. In a method of making an aqueous explosive which comprises intermixing the components of said explosive to form a continuous stream where at least one of said components is a gas-retaining component, a method of controlling the density of said explosive comprising continuously mixing at least one of said components including said gas-retaining component and a gas in a mixing zone, maintaining a pressure drop of at least 5 p.s.i. across said mixing zone, and homogeneously dispersing said gas in said gas-retaining component in said mixing zone.

2. In a method according to claim 1, the improvement comprising discharging said aqueous explosive to the atmosphere at a pressure at least about 5 p.s.i. greater than atmospheric pressure after said explosive has passed through said mixing zone.

3. In a method according to claim 1, the improvement comprising admitting said gas to said stream at a pressure of at least about 5 p.s.i. greater than the pressure of said stream at the point of addition of said gas.

4. A method according to claim 1 wherein said gas is air.

5. A method according to claim 1 wherein said explosive composition has a crystallization temperature above its foam point.

6. A method according to claim 1 wherein said explosive is in the form of an emulsion.

7. A method according to claim 1 wherein said gas-retaining component is a fuel.

8. A method according to claim 1 wherein said component constitutes about 0.5 to 15 percent sive and has a viscosity of at least about 1,000 68 F.

9. In a method of making an aqueous explosive which comprises intermixing the components of said explosive to form a continuous stream where at least one of said components is a gas-retaining component, a method of controlling the density of said explosive comprising admittin a gas to at least a p ortlon of said components which ll'lC udes said gas-retaining component at a pressure of at least 5 p.s.i. greater than said portion, continuously mixing said portion and said gas in a mixing zone maintaining a pressure drop on said stream of at least 25 p.s.i. across said mixing zone, maintaining the flow of said gas into said portion at a constant rate regardless of variations in downstream pressure, and discharging said stream to the atmosphere at a pressure of at least 5 p.s.i. greater than atmospheric pressure.

10. A method according to claim 9 wherein said gas is air.

11. A method according to claim 9 wherein said explosive composition has a crystallization temperature above its foam point.

12. A method according to claim 9 wherein said explosive is in the form of an emulsion.

13. A method according to claim 9 wherein said gas-retaining component constitutes about 0.5 to 15 percent of said explosive and has a viscosity of at least about l,000 centipoises at 68 F.

14. A method according to claim retaining component is a fuel.

gas-retaining of said explocentipoises at 13 wherein said gas- 

2. In a method according to claim 1, the improvement comprising discharging said aqueous explosive to the atmosphere at a pressure at least about 5 p.s.i. greater than atmospheric pressure after said explosive has passed through said mixing zone.
 3. In a method according to claim 1, the improvement comprising admitting said gas to said stream at a pressure of at least about 5 p.s.i. greater than the pressure of said stream at the point of adDition of said gas.
 4. A method according to claim 1 wherein said gas is air.
 5. A method according to claim 1 wherein said explosive composition has a crystallization temperature above its foam point.
 6. A method according to claim 1 wherein said explosive is in the form of an emulsion.
 7. A method according to claim 1 wherein said gas-retaining component is a fuel.
 8. A method according to claim 1 wherein said gas-retaining component constitutes about 0.5 to 15 percent of said explosive and has a viscosity of at least about 1,000 centipoises at 68* F.
 9. In a method of making an aqueous explosive which comprises intermixing the components of said explosive to form a continuous stream where at least one of said components is a gas-retaining component, a method of controlling the density of said explosive comprising admitting a gas to at least a portion of said components which includes said gas-retaining component at a pressure of at least 5 p.s.i. greater than said portion, continuously mixing said portion and said gas in a mixing zone, maintaining a pressure drop on said stream of at least 25 p.s.i. across said mixing zone, maintaining the flow of said gas into said portion at a constant rate regardless of variations in downstream pressure, and discharging said stream to the atmosphere at a pressure of at least 5 p.s.i. greater than atmospheric pressure.
 10. A method according to claim 9 wherein said gas is air.
 11. A method according to claim 9 wherein said explosive composition has a crystallization temperature above its foam point.
 12. A method according to claim 9 wherein said explosive is in the form of an emulsion.
 13. A method according to claim 9 wherein said gas-retaining component constitutes about 0.5 to 15 percent of said explosive and has a viscosity of at least about 1,000 centipoises at 68* F.
 14. A method according to claim 13 wherein said gas-retaining component is a fuel. 